Circuit interrupting apparatus



May '7., 1940. H. A. TRIPLETT CIRCUIT INTERRUPTING APPARATUS Filed Oct.19, 1936 r i, l.' d 0.0 W /l//////Ml///Z/L/// z. L., .1.. .si, ....IT l.Y... 7..... V

l/ A fnv i Patented May 7, 1940 PATENT OFFECE CIRCUIT INTERRUPTINGAPPARATUS I Hugh A. Trplett, Wilmette, Ill., asslgnor to Schweitzer &Conrad, Inc., Chicago, Ill., a. corporation of Delaware ApplicationOctober 19, 1936, Serial No. 106,422

40 Claims.

My invention relates generally to electric circuit interrupters and ithas particular relation to fuses.

It is now well known to those skilled in the art that an arc drawnbetween the separable terminals of a circuit interrupter within a bodyof arc extinguishing material, such as magnesium hydroxide or boricacid, may be. extinguished by the gases which are evolved from thismaterial by the heat of the arc. Circuit interrupters have beenconstructed in which the arc extinguishing material is provided with twolongitudinal bores, one a main and centrally located bore and the otheran auxiliary bore of smaller diameter than and positioned parallel totheV main bore. An arcing terminal is provided in the main bore whichmay be retracted from the adjacent end terminal of the circuitinterrupter or fuse by a spring when the fusible element connectingthese terminals melts. If the current is relatively small, an arc isestablished in the auxiliary bore where a conductor is positionedhaving. one end connected to the arcing terminal and the other enddisposed in such relation to the adjacent end terminal as to form asmall gap therebetween. This gap is broken down on blowing of thefusible member or element and, as a result, the arc is extinguished inthe auxiliary bore rather than in the main bore. l

In a circuit interrupter of this type the main bore is so proportionedthat, under short circuit conditions when a relatively large flow ofcurrent takes place, the pressure due to the arc contacting andVaporizing the arc extinguishing material will not rupture the fusecontainer. When the short circuit interrupting requirements are met insuch a device, prompt circuit interruption is not obtained in the mainbore when the fault current is relatively small. This isdue Yto the factthat the relatively feeble arc does not make sufficient contact with thearc extinguishing material to release the required quantity of gas todeionize the arc stream at current zero. If the current causing thefusible element to melt is relatively great, such as that which flows onshort circuit, an arc will persist in the main bore. It Will beextinguished in the main bore by lengthening its path in this bore andby ample evolution of gases from the arc extinguishing material.

In my copending application, Serial No. 85,700, filed June 17, 1936, andassigned to the assignee of this application, I have disclosed a circuitinterrupter of the type described in which an arcing terminal iswithdrawn in a main bore in .a member formed of solid arc extinguishingmaterial,

extinguishing material.

the arcing terminal being held against the biasing force of the springby a strain Wire that is positioned in the auxiliary bore of the solidarc When the main fusible element, which is connected between the arcingterminal and the adjacent -end terminal, melts because of a fault in thecircuit, the entire flow of current is transferred to the strain wire inthe small bore. If. the current flowing as a result of the fault isrelatively small, the arc formed thereby will be readily extinguished inthe small bore. If the current in the arc that is required to beinterrupted exceeds the capacity of the auxiliary bore, the arc willrestrike in the main bore rand will be there extinguished because of theinherent capability of this bore for vextinguishing large current arcs.In a device of this character it is essential to provide some means forextinguishing low current arcs which cannot be effectively extinguishedin the main bore. In my copending application this problem has beensolved by positioning the strain wire in the auxiliary bore where thesmall current arcs are readily interrupted because of its inherentcapacity to interrupt such arcs.

Instead of permitting an arc to be formed and extinguished in the smallbore, it may be desirable to provide for merely increasing theresistanceof the shunt path after the current is shunted through it to a very highvalue, thereby obtaining a substantially arcless functioning of the fusewithin a certain range of operation. If

the current required to be interrupted is beyond this range ofoperation, an arc Will also persist in the main bore of they arcextinguishing material where it will be extinguished in the usualmanner.

A device which is inherently capable of. automatically increasing itsresistance to a very high value on flow of current therethrough isdisclosed in my copending application, Serial No. 669,955, filed May 8,1933, and assigned to the assignee of this application, no w Patent2,066,129. As there disclosed I have provided a variable resistantelement which has the characteristic of cumulatively .increasing its'ownresistance, not merely by the thermal coeflcient of resistance which isa property of the metal employed, but by a chemical union with a reagentwhich is liberated by the heat generated by the element. This reaction,4which produces a permanent change, reduces the element from a conductorto a non-conductor, without arriving at the stage of forming free metalvapor as a part of the current carrying path. In general, the variableresistance element comprises a tungsten conductor in the form of a coilwhich is embedded in a powdered compound, preferably comprising calciumcarbonate. On being heated the tungsten wire reacts with the calciumcarbonate in such manner as to be transformed from a conductor to anon-conductor. In this copending application I have disclosed thisvariable resistance ele- 'ment in combination with a circuit interrupterof the liquid arc extinguishing type. The variable resistance elementserves to assist the interrupter in extinguishing large current arcs,the interrupter itself being inherently capable of extinguishing smallcurrent arcs. The variable resistance element is not called upon tofunction except in the event that the current required to be interruptedexceeds a relatively small value which can be readily interrupted by thecircuit interrupter. The large fault current flowing causes the tungstenconductor-to be heated to y such an extent that it reacts with thesurrounding calcium carbonate and it changes its characteristic to thatof a non-conductor, during which change the current flow in the circuitlis correspondingly reduced without arcing, except as an arc is formedbetween the relatively movable terminal members of. the circuitinterrupter.

It is one of the objects of my present invention to combine theoperating features of the variable resistance element with a circuitinterrupter of the type which depends for its operation upon the blastaction on an arc drawn in a restricting bore of fixed diameter and to soarrange and connect the variable resistance element that it will beeffective to interrupt low current faults which cannot be effectivelytaken care of in the large bore.

The principal object of my invention is to accomplish prompt circuitinterruption at low valuesv of current which cannot be expeditiouslyinter-- rupted in the main bore.

An impo ant object of my invention is to accomplish circuit interruptionwithout the necesvide for connecting a refractory metalconductorembedded in a powdered compound between the arcing terminal andthe adjacent terminal of a fuse of the solid arc extinguishing materialtype to offer a path for the flow of current in the shunt circuit thusformed while the arcing terminal is being retracted by its spring, thepath being changed to a non-conductor by the action of the currentflowing through it.

Other objects of my invention will in part be obvious and in part appearhereinafter.

My invention, accordingly, is disclosed in the embodiment hereof shownin the accompanying drawing and it comprises the features ofconstruction, combination of elements and arrangement of parts whichwill be exemplified in the construction hereinafter set forth and thescope of the application of which will `be indicated in the appendedclaims.

For a more complete understanding of the nature and scope of myinvention reference may be had to the following detailed descriptiontaken in connection with the accompanying drawing, in

which:

Figures 1 and 2, taken together, show a concrete embodiment of myinvention, Figure l illustrating one end of the fuse and Figure 2illustrating the other end; and

Figure 3 is a detail cross-sectional view of a modified connection forthe shunt circuit.

According. to my invention the arc extinguishing material, such asmagnesium hydroxide or boric acid, of a circuit interrupter is provided4with a single bore in which the arcing terminal rounded with a fillingof a powdered compoundA comprising calcium carbonate in which isembedded a conductor in the form of a coil which may be tungsten. Oneend of the coil is connected electrically to the arcing terminal whilethe other end may either be disposed in insulated spaced relation to orelectrically connected to the end terminal of the interrupter adjacentthe arcing terminal. When the fusible element and the strain wire arefused on the occurrence of sufficient overload to effect this operation,the slight gap between the end of the coil and the adjacent fuseterminal is broken down, if the gap is used, and current f'lows Ithroughthe tungsten coil while the arcing terminal is being withdrawn in thebore to a safe distance against restriking. If the gap is not used, thenthe main current is immediately shunted through the coil in addition tothe relatively small current already fiowing therethrough. The flow ofcurrent through the tungsten coil with the resulting heating andchemical effects causes in either case a rapid change of the metallicconducting path to one which is essentially non-conducting without theformationV of an arc as described in my copending application, SerialNo'. 669,955, referred to hereinbefore.

In the vevent that the current required to be interrupted is greaterthan that which can be handled by the shunt conductor, an arc willpersist n the main bore between the arcing terminal and the adjacent endterminal which will be extinguished in the usual manner by the evolutionof gases from the arc extinguishing material. In this case the tungstencoil will 'oe converted to a non-conductor but it will perform no usefulfunction.

Referring now particularly to the drawing, it will be observed that acircuit interrupter, shown generally at 10, is provided which has theabove described advantages and operating'characteristics. The circuitinterrupter 1li comprises a housing or fuse tube 1|, shown forillustrative purposes as being composed of glass, having at its upperend an upper ferrule 12 provided with upwardly extending spring fingers1I which may be integrally formed therewith. The ferrule 1! may bemachined from a solid brass rod and slots are milled diametricallyopposite each other to provide the spring fingers 13. Since thesectional view is taken through a pair of these slots, the fingers 13are shown in elevation. At the u means.

a retaining ring 86 is provided with external lower end of the fuse tube1I a lower ferrule 14 is provided having a cap threaded into it, asillustrated. The cap 15 has secured thereto a spring and cable fastener18 to which a cable I6 and a spring i1 may be connected. The cables i8and the spring i1 have a spring and cable fastener 22 at their upperends. The foregoing described parts of the fuse 19 form the portionthereof into which a cartridge, shown generally at 11, may be insertedto provide a fuse of the renewable element type. Y

It will be observed that the cartridge 11 comprises a cartridge tube 18which may be fiber, but which preferably is made of fiber paperimpregnated with Bakelite and rolled into a sleeve and cured. The tube18 extends downwardly to provide' a shield around the upper end of thespring i1. A cartridge ferrule19 is mounted on the upper end of thecartridge tube 18 and is secured in engagement therewith by pins 88. A

shoulder nut 8i is threaded on the upper end of Y the cartridge ferrule19 for cooperating with the spring fingers 13 to secure the cartridge 11in operative position and to facilitate unloading without blowing of thefusible element 93 and the strain wire 98. Inside of the cartridge tube18 an arcing tube 82 is provided which may be formed of an areextinguishing material such as magnesium hydroxide, boric acid or thelike, and which will evolve a gas in the presence of an are to assist inextinguishing the arc. The arcing tube 82 may be formed as a continuoustube or it may be sectioned, if desired. A single bore 83 is provided inthe center of the arcing tube 82 as illustrated. The arcing tube 82 maybe secured in' position in the cartridge tube 18 by means of a metalliccartridge washer 84 which is fastened to the inner walls of thecartridge tube 18 by pins 85 or any other suitable At the upper end ofthe arcing tube v82 threads for engaging the interior threads of thecartridge ferrule lil.` The retainingring 88 is formed of an insulatingmaterial such as ber and is provided with a frusta-conical opening, asillustrated, to provide an arcing chamber.

An arcing terminal 81, rod-like in shape and preferably formed ofcopper, is positioned inside of the bore 83 with a slight clearance topermit free movement and is disposed to be retracted by the spring il towhich it is connected by the spring and cable fastener 22. The lower endof the arcing terminal 8i is threaded int'o the spring and cablefastener 22 as will be readily understood. in order to prevent thearcing terminal il from turning relative to the cartridge washer M; itslower end is provided with a hexagonal nut 88 that is arranged tointeriit with a corresponding opening in the lower surface of thecartridge washer tft. Contact with the arcing terminal till ismaintained by means of a garter spring 89 positioned around it in asuitable groove in the cartridge washer te. llt i's desirable tomaintain an electrical connection between the arcing terminal 8l and thecartridge lwasher tt as the former is moved through the latter for apurpose which will be apparent h'ereinafter.

The arcing terminal 8l is held againstthe retractive force of the springi1 by means of a strain wire 98 which may be looped over a transversepin 9i in the cartridge ferrulel 19 and a pin 92 that extendstransversely through a slot in the upper end of the arcing terminal 81.A main fusible element or Wire 93, preferably in ling 91.

the form of a coil of silver wire, is connected between the upper end ofthe arcing terminal 81 and the cartridge ferrule 19. One end of thefusible element 93 is secured in a suitable opening in the upper end ofthe arcing terminal 81 which may be peened over or otherwise se curedthereto while the other end is threaded through a suitable opening inthe cartridge ferrule 19 and the walls of the opening are distorted, asby means of a -prick punch or the like, to pinch them into goodelectrical contact with the upper end of the fuse wire 93.

With a view to providing a shunt path around the arc which is formedwhen the fusible element 93 and the strain wire 90 are melted, whichshunt path may be reduced to a non-conductor by the action of thecurrent flowing through it, a filling 94 of solid material such as apowdered compound is positioned around the arcing tube 82 and between itand the inner wall of the cartridge tube 18. The powdered compound iscomposed principally of calcium carbonate in the form of limestone ormarble dust and it has embedded therein a conductor 95 in the form of a.coil, one end of which is connected by any suitable means to thecartridge washer 84, while the other end extends through a suitableopening 98 in the cartridge ferrule 19, where it may be insulatedtherefrom by an insulating bush- The conductor 95 is formed preferablyof tungsten, although it may be formed of molybdenum, tantalum, or asimilar metal of a class which has a high melting point and which, whenraised to a high temperature will evolve from the compound 98 a suitablereagent and combine therewith. In its original form the resistance ofthe conductor 95 is relatively low. However, when it is heated to a hightemperature, it will react with the powder 94 in such manner as tochange-lts characteristics from that of a conductor to that of anon-conductor.

It will now be apparent that no-deterioration of Y the conductor 95takes place during normal operation of the interrupter because it isinsulated at its upper end from the cartridge ferrule 19. However, thegap therebetween is slight and may be readily broken down by increasedvoltage drop on melting of the strain wire 98 and the fusible element93.

It will be apparent that the upper end of the conductor 85 may be sopositioned with respect to the cartridge ierrule i9 as to position thegap therebetween in the path of the ionized gases that are formed onblowing of the fusible element 93 and the strain wire fit. The gap wouldthen be more readily broken down because of the conducting path thereinformed by the ionized gases.

lit may be desirable to provide a metallic connection between the upperend of the conductor 9b and the cartridge ferrule 19, thereby providinga permanent metallic shunt path around the strain wire itt and thefusible element 98. Fon

lthis purpose a metallic bushing 91' may be employed, as shown in Figure3, and positioned in the opening tt. The bushing 91 may be formed of asuitable conducting material, such as copper or brass, and it may beswaged about the conductor @it and driven intoV the opening 98 toprovide. good electrical contact with the cartridge ferrule 19. In thisembodiment of the invention the conductor 95 carries a slight amount ofcurrent during normal operation but this current is not sumcient tochange its resistance. It is only after the fusible element 93 and thestrain wire 98 are fused, that sufficient current flows through theconductor 99 to change its resistance characteristics.

A cross pin 99 is positioned across the cartridge fcrrule 19 to providefor engagement with a suitable tool for drawing the cartridge 11 throughthe fuse tube 1I and placing it in the operative position as shown inthe drawing.

The cartridge 11 may be connected to the spring I1 and the cables I9 byscrewing the arcing terminal 81 into the upper cable fastener 22. 'I'heassembly may then be positioned in the fuse tube 1I and the cap 15 maybe screwed into place. A suitable tool, somewhat in the form of a buttonhook, is inserted through the other end of the fuse tube 1I to engagethe pin 99 and draw up the cartridge 11 to the position illustrated inthe drawing. In this position the shoulder nut 9i is in engagement withthe upper ends of the spring fingers 13 and the cartridge 11 is therebyprevented from moving inwardly under the influence of -the tensionspring I1'. A clamp nut 99 may then be screwed onto the threadedportions of the spring fingers 13 for locking vthem in position. It willbe observed that the clamp nut 99 is provided with an internal taperedclutch surface which, when drawn tight on the threads, forces the springfinger 13 radially inwardly to engage the cartridge ferrule 19 with aclutching action and provide a good electrical connection between the'fusible element 93 and the upper ferrule 12.

In operation, when a predetermined overload occurs in a circuit in whichthe interrupter 19 shown in Figures 1 and 2 is connected, the fusibleelement 93 melts and shunts the current to the strain Ywire 99, whichalso melts, thereby releasing the arcing terminal 91 for movement underthe iniiuence of spring I1. An arc is then formed between the cartridgeferrule 19 and the arcing terminal 91, as the latter is retracted withinthe bore 93 of the arcing tube 92. A sufficient voltage will then beimpressed. following the first current zero of arcing, between thecartridge ferrule 19 and the upper end of the conductor 89 to break downthe gap formed. by the insulation bushing 91 and consequently currentwill flow through the conductor 99. Since the conducting path throughthe conductor 99 will now be of relatively low resistance, the arc willnot persist in the bore 93. The current flow, now shunted through theconductor 99, will heat it to a sufficiently high temperature to causereaction with the powdered compound 94 and change its characteristics tothose of a non-conductor.

Meanwhile the arcing terminal 91 in the Bore 93 has been withdrawn to asafe distance against restriking by the spring I1 and interruption hasbeen accomplished without arcing except for the initialarc formed by thefusion of the fusible lelement 93 and the strain wire 99. Because of theprovision of the garter spring 89 in the cartridge washer 94, the lowerend of the coil 99 ls maintainedy in continuous conducting engagementwith the arcing terminal 91. 'Ihis insures a complete conducting pathbetween the ferrules 12 and 1'4 through the conductor 99 for the lowcurrent interrupting condition.

If the interrupter 19 is called upon to interrupt an overloadapproaching a short circuit, the arc will persist in the bore 93, whereit will be extinguished by the lengthening of its path and the gas whichis evolved from the arcing tube 92.

When the construction shown in Figure 3 is used in conjunction with theremaining parts 0f the interrupter 19, illustrated in Figures 1 ari 2,the entire current immediately flows through the conductor 89 on meltingof the fusible element 93 and the strain wire 90 and no arc is formed inthe bore 93, since the gap is not present and the conductor 99 forms apart of a metallic circuit shunting the fusible element 93 and thestrain wire 99. The conductor 99 then looses its conducting qualitiesand changes, as described hereinbefore, to have the characteristics of anon-conductor. For low fault currents, this construction providesarcless circuit interruption.

If desired, the fuse tube 1| may be of such a length that the arcingterminal 91 will be completely withdrawn from the arcing tube 92 and 1moved out of contact engagement with the garter spring 89 and thecartridge washer 94. This operation may be desired for the purpose ofcompletely insulating the ferrule 14 from the ferrule 12 after the fusehas operated on a low current fault. After the interrupter 19 hasoperated, the resistances of the auxiliary circuit and of the surface ofthe 'bore 93 are very high but a complete withdrawal of the terminal 91from the washer 84 insures increased protection against reestablishmentof a conducting path along the surface of tube 19.

After the fuse device 19 has operated to interrupt the circuit, thecartridge 11 may be removed and replaced with a new one of suitablecurrent carrying capacity. The fuse device 19 will then be capable ofagain interrupting the circuit in the manner herein set forth on theoccurrence of an overload condition.

The fuse device 19 has been shown and described with the arcing terminal81 located at the upper end. It will be obvious that the position of thefuse device 19 may be reversed and that the circuit would then beinterrupted at the lower end. This is the preferred position formounting the fuse device 19 for operation. However, for purposes ofillustration, it has been shown in the up and down position.

Since certain further changes may be made in the foregoing constructionsand different embodiments of the invention may be made without departingfrom the scope thereof, it will be understood that all matter shown inthe accompanying drawing or described hereinbefore shall be interpretedas illustrative, and not in a limiting sense. t

I claim as my invention:

1. The combination, with a circuit interrupter depending for itsoperation upon the blast action on an arc drawn in a restricting boreformed in a solid arc extinguishing material, of a circuit in parallelwith said circuit interrupter for interrupting currents smaller than thecurrents readily interrupted in said bore, said parallel circuitincluding a conductor the resistance of which increases to a relativelyhigh value by the action of the current flowing through it.

2. The combination, with a circuit interrupter depending for itsoperation upon the blast action on an are drawn in a restricting boreformed in a solid arc extinguishing material, of a circuit in parallelwith said circuit interrupter for inter-V rupting currents smaller thanthe currents readily interrupted in said bore, said parallel circuitcomprising a metallic conductor arranged and adapted to increase itsresistance rapidly and to be converted to a non-conductor by th'e actionof the current flowing through it.

3. The combination, with a circuit interrupter depending for itsfunctioning upon the blast action on -an arc 4drawn in a restrictingbore formed in a solid arc extinguishing material from which gases areevolved by the heat of the arc, of a parallel circuit around saidcircuit interrupter for interrupting currents smaller than the currentsreadily interrupted in said bore by said blast action, said parallelcircuit including a conductor the resistance of which increases to arelatively high value by the action of the current iiowing through it,ancl means preventing current flow through said conductor during normaloperation.

4. The combination, with a circuit interrupter depending forv itsfunctioning upon the blast action on an arc drawn in a restricting boreformed in a solid arc extinguishing material from which gases areevolved by the heat of the arc, oi a parallel circuit around saidcircuit interrupter for interrupting currents smaller than the currentsreadily interrupted in said bore by said blast action, said parallelcircuit including a conductor the resistance of which increases to arelatively high value by the action of the current iiowing through it,and means including an arc gap connected in series with said conductorfor preventing current flow therethrough during normal operation.

5. The combination, with a circuit interrupter depending for itsfunctioning upon the blast action on.- an arc drawn in a restrictingbore formed in a solid arc extinguishing material from which gases areevolved by the heat of the arc,

` of a parallel circuit around said rcircuit interrupter forinterrupting currents smaller than the currents readily interrupted insaid bore by said blast action, 'said parallel circuit comprising ametallic conductor arranged and adapted to rapidly increase itsresistance and to be converted without fusing to a non-conductor by theaction of the current flowing through it, and means in'- cluding an 'arcgap connected in series with said conductor for preventing current flowvtherethrough during normal operation.

6. In a circuit interrupter, in combination; a rst interrupting meansarranged and adapted to interrupt large currents and comprising'a tubeformed of solid arc extinguishing material and a rod-like terminalmembermovably mounted in the bore of said tube, lcurrent interruptionbeing eected by a free flow toward the open end of said bore of gasesevolved from its inner wall by the action of the arc thereon; and asecond interrupting means arranged and adapted to interrupt smallcurrents, in parallel with said first eflected by a free flow toward theopen end of said bore of gases evolved from its inner wall by the actionof the arc thereon; a second interrupting means arranged and adapted tointerrupt small currents,` in parallel with said first interruptingmeans and comprising a metallic conductor embedded in a mass ofinsulating'material, current interruption in said second, interruptingmeans being effected on conversion 'of said metallic conductor to anon-conductor by reaction therewith of said insulating material causedby heat generated by current flow through said conductor;

and means preventing current dow through said 'said bore of gasesevolved from its inner Wall by the action of the arc thereon; Ia secondinterruptin g means arranged and adapted to interrupt l small currents,in parallel with said rst interrupting means and comprising a metallicconductor embedded in a mass of insulating material, and an arc gapconnected in series with said conductor to prevent current iiowtherethrough while normal load current ilows through said rstinterrupting means, current interruption in said second interruptingmeans being effected by breaking down of said arc gap on operation ofsaid first interrupting means and conversion of said metallic conductorto a non-conductor by reaction therewith of said insulating materialcaused by heat generated by current flow through said conductor.

9. In a circuit interrupter,x in combination, a main fusible element ofsilver normally out of contact with surrounding materials and arrangedand adapted to fuse upon overload of a predetermined value causing theinterrupter to operate, means dependent upon the blast action of gasesevolved from a solid arc extinguishing material and disposed toextinguish arcs of large current value formed by fusingk of said silverelement but not arcs of low current value, an auxiliary element oftungsten disposed to shunt said silver element and normally closelysurrounded by an insulating material, said tungsten element on increasedflow of current therethrough being conv-verted to a non-conductor bychemical action with said surrounding material for interruptingoverloads of low value.

10. In a circuit interrupter, in combination, a iirst interrupting meansarranged and adapted by its calibration to control the operation of theinterrupter, and to eiectively extinguish large overload arcs and beingrelatively ineffective to -extinguish small overload arcs, a secondinterrupting means disposed to be connected in shunt with said iirstinterrupting means and comprising a metallic circuit closely embedded inan insulating material and arranged and adapted to react therewith, toprevent the formation of appreciable arcs by low overloads in said rstinterrupting means and to interrupt these low overload arcs effectivelyafter the operation of said first interrupting means.

11. A -circuit interrupter comprising, in combination, a housing havingflxedterminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in the other end vof said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted by said spring, fusible means connecting saidarcing terminal and the adjacent iixed terminal, and chemical fuse meansdisposed to be connected between said arcing and adjacent terminals whensaid fusible means melts.

12. A circuit interrupter comprising, in comblnation, a housing havingxed terminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in the other end of said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted by said spring, a main fusible elementconnecting said arcing terminal and the adjacent fixed terminal, astrain wire for holding said arcing terminal against the force of saidspring, and a chemical fuse element the resistance of which increases toa relatively high value on being heated to a predetermined temperaturearranged and adapted to be connected between said arcing and adjacentterminals when said main fusible element. blows.

13. A circuit interrupter comprising, in combination, a housing havingfixed terminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in the other end of said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted by said spring, main fusible means connectingsaid arcing terminal and the adja-l cent fixed terminal, and a chemicalfuse element disposedto be connected between said arcing and adjacentterminals when said main fusible means melts, said chemical fuse elementcomprising a conductor and an associated reagent for reacting therewithto become substantially nonconductive on being heated to a temperaturesuicient to initiate a reaction.

14. A circuit interrupter comprising, in combination, a housing havingfixed terminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in the other end of said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted by said spring, a main fusible elementconnecting said arcing terminal and the adjacent fixed terminal, astrain wire for holding said arcing terminal against the retractileforce of said spring, and a chemical fuse element arranged and adaptedto be connected between said arcing and adjacent terminals when saidmain fusible element and strain wire melt, said '4 chemical fuse elementcomprising a conductor and an associated reagent for reactingtherewith-to become substantially non-conductive on being heated to atemperature suiilcient to initiate a reaction.

15. A circuit interrupter comprising, in combination, a housing havingfixed terminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in the other end of said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted b'y said spring, a main fusible elementconnecting said arcing terminal and the adjacentxed terminal, and achemical fuse element disposed to be connected between said arcing andadjacent terminals when said main fusible element blows, said chemicalfuse element comprising a powdered compound surrounding said body of arcextinguishing material and a conductor of refractory metal embeddedtherein, said conductor reacting with said compound to becomesubstantially non-conductive on being heated to a temperature sufficientto initiate the reaction.

16. A circuit interrupter comprising, in combination, a housing havingfixed terminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in the other end of said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted by said spring, a main fusible elementconnecting said arcing terminal and the adjacent fixed terminal, apowdered compound surrounding said body of arc extinguishing material,and a coil ofl refractory metal embedded in said compound, one end ofsaid coil being connected to said arcing terminal and the other endbeing disposed in insulated spaced relation to said A adjacent fixedterminal.

17. In a circuit interrupter, in combination, a first interrupting meansarranged and adapted by its vcalibration to control the operation of theinterrupter, and to effectively extinguish large overload arcs by theblast action of gases formed by the action of these arcs upon a solidarc extinguishing material and being relatively ineffective toextinguish small overload arcs, a second interrupting means disposed tobe connected in shunt With said first interrupting means and comprisinga metallic circuit closely embedded in an insulating material andarranged and adapted to react therewith to prevent the formation ofappreciable arcs by low overloads in said first interrupting means andto interrupt these low overload arcs effectively after the operation ofsaid first interrupting means.

18. A circuit interrupter comprising, in combination, a housing havingfixed terminals, a tension spring in one end of said housing, a body ofsolid arc extinguishing material in .the other end of said housingprovided with a longitudinal bore, an arcing terminal in said boredisposed to be retracted by said spring, a main fusible elementconnectingsaid arcing terminal and the adjacent xed terminal, a powderedcompound surbers for connection in anelectric circuit, a fusible elementinterconnecting said terminal members, a member of solid arcextinguishing mate-` rial having a bore therein, means for moving one ofsaid terminal members through said bore on melting of said fusibleelement, and a variable resistance element arranged and adapted to beconnected between said terminal members when said fusible element melts,the resistance of said variable resistance element increasing to arelatively high value as a function of current flow therethrough.

20. A circuit interrupter comprising, in combination, a pair of spacedapart terminal members for connection in an electric circuit, a fusibleelement interconnecting said terminal members,

a member of solid arc extinguishing material having a bore therein,means for moving one of said terminal members through said bore onmelting of said fusible element, and auxiliary circuit means parallelingsaid fusible element and conducting current between said terminalmembers when said fusible element melts, said auxiliary circuit meansincluding a conductor of refractory metal embedded in a powderedcompound, said conductor reacting with said compound to becomesubstantially non-conductive on being heated by current flowtherethrough to a temperature sulcient to initiate the reaction.

21. A circuit interrupter comprising, in combination, a pair of spacedapart terminal members for connection in an electric circuit, a fusibleelement interconnecting said terminal members, a member of solid arcextinguishing material having a bore therein, means for moving one ofsaid terminal members through said borel current in a circuitinterrupter inherently capable of effectively interrupting largecurrents which comprises shunting the entire current through anauxiliary circuit and automatically increas-` ing the resistance of saidauxiliary circuit to a relatively high value as a function of thecurrent iioW therethrough.l

23. The method of interrupting current flow in a circuit in which acircuit interrupter is connected that is capable of interrupting arcscaused by large current flow in said circuit but not arcs caused bysmall current iiow which comprises opening the circuit interrupter,shunting the small current through an auxiliary circuit, andautomatically Vincreasing the resistance of the auxiliary circuit to arelatively high value as a function of the current flow therethrough.

24. In a circuit interrupter, in combination; a iirst interrupting meansarranged and adapted to interrupt large currents and comprising a tubeformed of insulating material and a rodlike terminal member movablymounted in the bore of said tube, current interruption being effected bya free flow toward the open end of said bore of gases evolved from itsinner wall by the action of the arc thereon; and a second interruptingmeans arranged and adapted to interrupt small currents, connected inparallel with said first interrupting means and comprising al metallicconductor embedded in the wall of a tube of insulating material, currentinterruption in said second interrupting means being effected onconversion of said metallic conductor to a non-conductor by reactiontherewith of said insulating material'caused by heat generated bycurrent flow through said conductor, said tube of insulating materialbeing positioned around said bore and separating it from said secondinterrupting means whereby the arc drawn in said bore does not aiect thefunctioning of said metallic conductor.

25'. In a circuit interrupter, in combination; a first interruptingmeans arranged and adapted to interrupt large currents and comprising atube formed of insulating material and a rod-like terminal membermovably mounted in the bore of said tube, current interruption beingeffected by a free iiow toward the open end of said bore of gasesevolved from its inner wall by the action of the arc thereon; a secondinterrupting means arranged and adapted to interrupt small cur= rents,connected in parallel with said first interrupting means and comprisinga metallic conductor embedded in the wall oi a tube ci' insum latingmaterial, current interruption in said secterrupted whereby thelikelihood of an arc restrlking through either of said circuitinterrupters is reduced to a minimum.

26. A rell unit for a circuit interrupter, inclding. a sleeve ofinsulation having terminal members at the ends thereof andva tensionspring disposed at one end, fastened at one end to the adjacent terminalmember and provided with a coupling at the other end, comprising, incombination; a first interrupting means arranged and adapted tointerrupt large currents and comprising a'tube of solid arcextinguishing material and a rod-like terminal member movable in thebore of said tube, current interruption being eifected by a free flowtoward the open end of said bore of gases evolved from its inner wall bythe action of the are thereon; and a second interu rupting meansarranged and adapted to inter rupt small currents, connected in parallelwith` said first interrupting means and comprising a metallic conductorembedded in a tubular mass: of insulating material disposed around saidtube' of solid are extinguishing material, current interruption beingeiected on conversion or said metallic conductor to a non-conductor bywww action therewith of said insulating material caused by heatgenerated by current flow through said conductor; 4both saidinterrupting means being adapted to be positioned in the other end ofsaid sleeve, and one end of said rod-like terminal member being adaptedto be readily connected to said coupling and the other end beingconnected by a fusible element to the adjacent end terminal member.

27. A refill unit for a circuit interrupter, including a sleeve ofinsulation having terminal members at the ends thereof and a tensionspring disposed at one end, fastened at one end to the adjacent endterminal member and having a threaded coupling at its other end,comprising, in combination, a fiber tube disposed to be positioned inthe other end of said sleeve,a tube of solid are extinguishing materialin said fiber tube, a rod-like terminal member movable in the bore ofsaid tube of solid arc extinguishing material and threaded at its innerend for connection to said threaded coupling, fusible means at the otherend of said rod-like terminal member, an annular layer of insulatingmaterial between said tubes, a conductor in the form of a coil embeddedin said layer and adapted to react therewith and to increase itsresistance on being heated by now of current therethrough,I an annularterminal member at the outer end of said fiber tube to permit clampingto the adjacent end terminal member of said sleeve, and an intermediateterminal member at the inner end of said tube of arc extinguishingmaterial, ithe circuits through said iusible means and said coil beingconnected in parallel between said annular and intermediate terminalmembers.

28. The combination, in a circuit interrupter depending for itsoperation upon the blast action on an arc drawn in a restricting bore ofxed diameter, of a rod-like terminal member movable in said bore, meansfor withdrawing said terminal member, and means for maintaining conntact engagement with said terminal member during a predetermined portionofdts movement through said bore.

29. In a fuse, in combination, a rst solid arc extinguishing materialadapted to assist in interrupting large overload currents by blast action on an arc drawn in a bore therein, and a second solid arcextinguishing material adapted to assist in interrupting small overloadcurrents by chemical action on a metallic conductor closely embeddedtherein.

30. In a fuse, in combination, a first solid arc extinguishing materialadapted to interrupt current flow by blast action on an arc drawn in abore therein, and a second solid arc extinguishing material adapted tointerrupt current ilow by chemical action on a metallic conductorembedded therein.

31. In a fuse, in combination, a ilrst solid arc extinguishing materialgenerally tubular in form and adapted to interrupt current ow by blastaction on an arc drawn in the bore thereof, and a second solid arcextinguishing material concentrically disposed with respect to saidfirst solid arc extinguishing material and adapted to interrupt currentflow by chemical action on a metallic conductor embedded therein.

32. In a fuse having a terminal adapted to be moved away from anotherterminal on blowing of the fuse, in combination, a ilrst'means arrangedand adapted to evolve an arc extinguishing medium by the heat of an arcdrawn between said terminals, a second means in parallel with said rstmeans and arranged and adapted to interrupt current flow by increasingits resistance as a result of chemical reaction, and

means for maintaining circuit connectionv between said second means andthe movable terminal while it is moving away from the stationaryterminal.

33. In a fuse having a terminal adapted to be moved away from anotherterminal on blowing of the fuse, in combination, a first means arrangedand adapted to evolve an arc extinguishing medium by the heat of an arcdrawn between said terminals, a second -means in parallel with saidrstmeans and arranged and adapted to interrupt current flow byincreasing its resistance as a result of chemical reaction, and meansfor maintaining circuit connection between said second means and themovable terminal while it is moving away from the stationary terminal,said movable terminal being completely withdrawn from said last namedmeans in the retracted position.

34. In a fuse having a rod-like terminal adapted to be moved through abore in a body of solid arc extinguishing material, in combination, anapertured metal'member through which the rod-like terminal is withdrawn,means for maintaining electrical connection between said metal memberand said terminal while the latter is being withdrawn, and meansproviding longitudinal movement oi' said terminal relative to said metalmember and preventing relative rotary motion during at least a portionof said longitudinal movement.

35. In a fuse having a rod-like terminal adapted to be moved through abore in a body of solid arc extinguishing material. in combination, ametal ring through which the rod-like.

terminal is withdrawn, means for maintaining electrical connectionbetween said metal ring and said terminal while the latter is beingwithdrawn, and means providing longitudinal movement of said terminalrelative to said metall ring and preventing relative rotary motionduring at least a portion of said longitudinal movement.

36. The combination, in a circuit interrupter depending for itsoperation upon the blast action on an arc drawn in a restricting boreoi' fixed diameter, of a rod-like terminal member movable in said bore,an apertured metal member through which said terminal member iswithdrawn, means for withdrawing said terminal member, and `re silientmeans interposed between said terminal member and said metal member tomaintain a ing said terminals having at least two sections one oi' whichis adapted to blow before the other on the occurrence oi' an overload tointerrupt the circuit between said terminals, a member biased formovement lengthwise of said housing, a strain element restraining saidmember and adapted to be released on blowing oi' one oi said sectionsfor releasing said member, and a body oi solid arc extinguishingmaterial individual to each o! said sections and disposed within saidcasing in sideby-side relation. 4

39. Ina fuse device of the dry type, in combination, a tubular casing ofinsulating material having terminals at its ends, conductor meansinterconnecting said terminals having at least two sections one of whichis adapted to blow betore theother on the occurrence of an overload tointerrupt the circuit between said terminals, a plunger biased formovement lengthwise of said housing, a strain element restraining saidplunger and adapted to be released on blowing of said one section i'orreleasing said plunger, and a body oi' solid arc extinguishing materialindividual to each of said sections and disposed within said casing inside-by-side relation, one of the bodies oi' solid arc extinguishingmaterial at least being formed by a granular material.

40. In a fuse device, in combination, a tubular casing of insulatingmaterial having terminals at its ends, a plurality of coextenslve bodiesoi' solid arc extinguishing material within said housing at least one ofwhich comprises arc extinguishing material in granular form, conductormeans interconnecting said terminals having at least two sections eachindividual to one o! said bodies of arc extinguishing material and oneoi' which blows before the other on the occurrence of an overload tointerrupt the circuit between said terminals, a member movablelengthwise of said housing, spring means biasing said member to effectmovement thereof, and a strain element restraining said member andadapted to be'released on blowing of said one section.

HUGH A. TRIPLE'I'I'.

lli

